Conventionally, a technique has been proposed for displaying a pattern according to a direction of light incident on a light guide plate which is formed into a plate shape and which has light transparency (see, for example, Patent Document 1).
For example, a light guide plate display device disclosed in Patent Document 1 includes a light guide plate, a plurality of light source devices provided along respective end faces of the light guide plate, and a plurality of prisms formed inside the light guide plate. The prisms respectively have a plurality of side surfaces facing the light source devices, and the side surfaces are respectively inclined in a thickness direction of the light guide plate at least in two stages by a transmissive inclined surface which transmits light radiated from the light source device, and a reflective inclined surface which reflects light radiated from the light source device and outputs the reflected light to a display surface of the light guide plate. Furthermore, a plurality of patterns is provided on the light guide plate. The prisms are formed such that, in each prism included in each pattern in the plurality of patterns, the area of the reflective inclined surface on the side surface facing the corresponding light source device is large and the area of the reflective inclined surface on the other side surfaces is small.